1. Field of the Invention
The present invention relates to a marine propulsion machine, such as an outboard motor having an outboard internal combustion engine or an outboard/inboard motor having an inboard internal combustion engine and, more particularly, to a drive shaft support structure built in a gear case for a marine propulsion machine.
2. Description of Background Art
A gear case, forming a lower part of a marine propulsion machine, defines a gear chamber therein for housing a bevel gear mechanism, used for transmitting power from a drive shaft to a propeller shaft. A drive shaft receiving bore extends downwardly from an upper end wall of the gear case, and the gear chamber is connected to the lower end of the drive shaft receiving bore. The drive shaft, extended through the drive shaft receiving bore, is supported for rotation in a bearing. Sufficient lubricating oil is contained in the gear chamber and the drive shaft receiving bore to lubricate the bevel gear mechanism placed in the gear chamber, and also to lubricate the bearing disposed in the drive shaft receiving bore.
A gear case of this general kind for a marine propulsion machine, disclosed in JP 8-34394 A, has a drive shaft receiving bore with an open upper end covered with the pump case of a water pump, to seal the drive shaft receiving bore and a gear chamber in a liquid-tight fashion.
In the gear case disclosed in JP 8-34394 A, a bearing is held between a flange of a drive shaft and the gear case, but is not fastened to the gear case. The bearing is held in place by gravity, and also by a downward thrust acting on a bevel gear included in a bevel gear mechanism. Since the bearing is not restrained from upward movement, it is possible that the bearing moves vertically together with the drive shaft.
The present invention has been made in view of such a problem as described above, and it is therefore an object of the present invention to provide a simple drive shaft support structure incorporated into a gear case for a marine propulsion machine, capable of sealing a gear chamber defined by the gear case in a liquid-tight fashion. It is another object of the present invention to provide a drive shaft support structure capable of fixedly holding a bearing in the gear case to restrain a drive shaft from vertical movement therein.